1. Field of the Invention
This invention relates to the shaping of glass sheets and, more particular, to the simultaneous shaping of two or more glass sheets biased against each other and an upper mold by vacuum.
2a. Technical Considerations
The techniques of sag bending to form shaped glass windows for automobiles and the like as discussed in U.S. Pat. No. 4,375,978 to Reese is well known. The glass sagging technique has been the method used to bend two glass sheets simultaneously, which sheets have subsequently laminated together to form a laminated automobile windshield. Glass sheets are positioned on a skeletal bending mold with a shaping rail that conforms to the shape and final configuration of the glass sheet to be shaped slightly inboard of the edge of the glass. The bending molds are then conveyed in succession through a heating lehr where the glass sheets are heated to their deformation temperature and begin to sag by gravity until the glass sheets conform to the configuration of the shaping rail. After the glass sheets have been properly deformed, the molds are conveyed through an annealing zone where the glass sheets are cooled in a controlled manner from their deformation temperature through their annealing range to anneal the glass sheets.
In order to fabricate more complex and deeper bend in the glass doublets used in windshields, the bending molds have been designed to include mold rails with articulated rail sections having end rail sections whose contours conform to the outline and shape desired for the longitudinal end portions of the glass sheets to be bent. The end rail sections are constructed and counterweighted to pivot downward into a lower position to support the mass of the relatively stiff flat glass sheets to be bent. When the glass sheets are softened by heat, the end sections pivot upward into an upper position where they cooperate with additional shaping rails to form a substantially continuous outline shaping surface conforming in contour and elevation to the shape desired for the glass sheets.
As automobile stylists demand even more complex shapes such as deep wraps and reverse curvature bends, press bending techniques have been used. Bending to such complicated shapes requires that the glass sheets be supported in precise alignment between upper and lower molds that are used to impart the different components of the complicated bends to which the glass sheets are to be shaped. In these doublet press bending techniques, the heat softened doublet is lifted off a ring bending mold pressed between upper and lower molds and redeposited onto the ring bending mold by the lower bending mold for subsequent processing, such as annealing.
2b. Patents of Interest
U.S. Pat. No. 3,846,104 to Seymour discloses a method and apparatus for shaping and cooling single glass sheets. Individual glass sheets are heated to their deformation temperature in a gas hearth furnace and conveyed into a glass shaping station, then a cooling station, and finally in a loading station. In the shaping station, the glass sheet is stopped in alignment with a lower ring mold that moves vertically between a recessed position and a raised position. The lower ring mold lifts the glass into engagement against an upper vacuum mold. The upper mold is evacuated to hold the shaped glass sheet thereagainst, while the lower mold is retracted downward. A tempering ring having an outline supporting surface conforming to the contour of the shaped glass sheet slightly inboard of the sheet periphery is brought into position between the upper and lower molds. The vacuum on the upper mold is released to deposit the shaped glass sheet on the tempering ring. The latter supports the bent glass sheet during movement to and residence at a cooling station. The tempering ring is then unloaded and returned to a position adjacent the shaping station to repeat the cycle.
U.S. Pat. Nos. 4,197,108 and 4,272,274 to Frank et al. disclose the use of a slotted glass sheet shaping mold capable of shaping glass sheets having different outlines, but bent to the same radius of curvature. The lower mold is comprised of a plurality of smoothly curved, upwardly facing, elongated shaping members extending continuously across the entire transverse dimension of the mold. The shaping members are separated by transversely extending grooves that extend completely across the entire transverse dimension of the shaping mold, having sufficient width and depth to permit clearance for raising the mold above a horizontal path of glass travel defined by glass conveying rolls. In operation, individual sheets of glass are serially conveyed through a furnace, heated to their deformation temperature and positioned over and lifted off the glass conveying rolls by the slotted mold into engagement with an upper vacuum mold. The slotted mold retracts into its lower position and the upper mold deposits the shaped glass on a tempering ring, moved into position beneath the upper mold, for movement of the sheet into the quench station and subsequent handling.
U.S. Pat. No. 4,229,200 to Seymour discloses drop forming hot glass sheets with auxiliary shaping means. Individual glass sheets are serially conveyed through a gas hearth furnace and heated to their deformation temperature. The heat softened glass sheets are then positioned below and lifted by a flat vacuum platen. Portions of the glass sheet are preshaped by auxiliary shaping means while the sheet is held against the platen. The glass sheet is then dropped onto a shaping ring to impart the complete desired curvature to the glass sheet. The shaped glass sheet is thereafter transferred to a cooling station.
U.S. Pat. Nos. 4,260,408, 4,260,409 and 4,265,650 to Reese et al. disclose a method of bending pairs of glass sheets. The pairs of glass sheets are positioned on ring-type outline bending molds and conveyed through a bending lehr where the glass sheets are heated to their deformation temperature. The glass sheet pair is sag bent in unison on the outline mold to bend the sheets to a shape approximating their final configuration. The pair of bent glass sheets is then lifted on a full face lower mold having the final desired shape for the minimum time sufficient to develop the final configuration. If necessary, the lower mold engages an upper pressing mold to sandwich the pair of glass sheets therebetween. The pair of bent glass sheets is returned as rapidly as possible to the outline mold and cooled at a controlled rate while supported on the outline mold to a temperature below the strain point to ensure that the pair of glass sheets retain their shapes so that they can be laminated subsequently with minimum difficulty.
U.S. Pat. No. 4,508,556 to Bennett et al. discloses a method and apparatus for bending glass sheets to complicated shapes. Individual sheets of heat softened glass are conveyed through a heating furnace and positioned in the shaping station on a gas hearth bed. A curved outline mold vertically lifts the glass sheet off the gas hearth bed and into contact with a shaped upper vacuum mold for forming. The outline mold retracts with the shaped glass sheet being held against the upper vacuum mold and a tempering ring shuttles into position beneath the upper mold. Vacuum is discontinued and the glass drops onto the ring which is transferred to the cooling station.
In all of these patents, either (a) a single glass sheet is shaped by an upper vacuum mold that holds the shaped glass sheet in contact thereagainst for subsequent deposition of the sheet on a tempering ring positioned thereunder or (b) a pair of glass sheets is preliminary sag bent on a bending iron and lifted off the iron by a lower mold and pressed between the lower and upper mold. The shaped pair of glass sheets is then redeposited on the bending iron for subsequent processing. It would be beneficial to provide a process wherein multiple plies of overlaying glass sheets could be formed between upper and lower molds, and the plies held in place by the upper vacuum mold as the lower mold is retracted.